Legal Liability: This is the biggest risk. If your KYC ends up tied to something serious like money laundering or terrorism, authorities won’t hesitate to go after you. And since it’s your name on the account, you can’t simply deny it, you already submitted your documents.
I think everyone should care and honor their name, so to sell personal data is completely out of consideration for me. Even if the payrate was high, that would definitely not worth it, because the weight of your credibility, reputation and name must be much beyond any material goods and prices.
However, I don't think there are potential legal issues on most cases, since it's quite difficult to prove someone sold their data. The most likely scenario is that the ID's owner is a victim who had their documents stolen by hacks from legit platforms they have signed up previously.